Television transmission system



Sept. 29, 1942. w. DILLENBURGER 2,297,451

TELEVISION TRANSMISSION SYSTEM Filed Aug. 9/1940 2 Sheets-Sheet 2 In ventor:

Patented Sept. 29, 1942 wUNlTED STATES PATENTOFFICE 2,297,461 TELEVISION TRANSMISSION SYSTEM Wolfgang Dillenburger, Berlin-Nikolassee, Germany; vested in the Alien Property Custodian Application August 9, 1940, Serial No. 351,934 In Germany November 25, 1938 derived from a positive image, and means for automatically changing the manner of amplification when the negative image is replaced by a positive image and vice versa. It is a further object to provide a transmitter adapted to scan alternatively positive films and negative films without requiring complicated adjustments and without impairing the quality and gradation of the received image.

According to the invention the amplifier arrangement is changed automatically when a negative image is scanned instead of a positive image, and vice versa. The automatic change is preferably controlled by a brightness value of the image or of the film itself. A portion of the film is used which in a positive film has a different opacity than the corresponding portion of a negative film. Preferably the strip of the film between successive images is employed as a controlling member because this strip is black or nontransparent in a positive film while it is white or transparent ina negative film.

When positive images are transmitted it is preferable to use amplifiers with a linear characteristic. If however negative images are to be reproduced as positive images, it is necessary to provide a converting stage in which the white portions of the image are reproduced as black por- 9 Claims. (Cl. 178-12) and means one andv the same transmission channel is used for the transmission of positive as well as negative images and the automatic change is effected by actuating a switching. arrangement, so that one and the same tube can be employed for the transmission of the positive images and of the negative images. For this purpose an amplifier stage with one or a number of tubes is used, the

amplifier having a curved characteristic line in normal operation so that it is suited for the transmission of negative images. If now positivev images are to be reproduced requiring a linear characteristic curve, the circuit arrangement is changed so that the same tubes operate as a cathode amplifier having a linear characteristic curve. In this manner it is possible to employ only one set of amplifier tubes for the positive images as well as the negative images.

Other aspects of my invention will be apparent or will be specifically pointed out in the descrip- -tion forming a part of this specification, but I do not limit myself to the embodiment of the inventions and vice'vers'a. Between the blackening of the image to be transmitted and the transparency of the film there exists the relation that the blackening is equal to the logarithm of the reciprocal value of the transparency. In consequence of this logarithmic function between the blackening and the transparency and in consequence of the conversion of white into black and black into white, it is necessary to use a transmission chan-.

nel having a logarithmic characteristic curve. and

a phase shift of 180 in order to produce the cor-- rect steps of the gradation in thepositive'received image.

tionherein described, as various forms may be adopted within the scope of the claims.

Referring to the drawings:

Fig. 1 shows a diagrammaticview of the television transmitting arrangement,

Fig. 2 is a circuit arrangement according to the invention,

Fig. 3 shows a modification of the circuit of Fig.

2, and

Figs. 4 and 5 are diagrams of the characteristic curve of the amplifier.

In Fig. 1 the film i is moved through a projector including a light source 2 and a condensing lens 3. The image of the film is reproduced by an optical arrangement 3 upon the photoelectric cathode of a television scanning tube 4. The signals produced in tube 4 are guided through line 5 to a control circuit 6 in which the transmission is automatically supervised. The output terminal of the scanning, tube 4 is furthermore also connected to the input circuit of an amplifier 8 and the amplifiers 8 and it are connected to further According to another feature of the invention 55 amplifying stages or to the the transmitter.

modulating stage of Fig. 2 shows in detail a circuit arrangement for carrying out the invention.

The image of the film l to be-transmitted is reproduced upon the photoelectric cathode l5 of the image transmitting tube 4. The image signals are taken off at the output terminal of the tube which may or may not contain a setoridary emission amplifier. The television signal currents pass through a resistor t5 so that image potentials can be taken off from the end of the resistor connected to the image tube. These image voltages are applied to a grid l1 of an amplifier tube l8. The cathode circuit of this tube contains a resistor l9 bridged by a condenser 29. The anode of tube i8 is connected to.

istic curves of the tubes differ from one another. The resulting slope of this tube arrangement can be made positive or negative by controlling the amplification factor of the tube having the larger maximal slope. The amplification factor is controlled by changing the potential of grid 39 of tube 31. The control voltage is derived a-resistor 2i and a condenser 22. The other side of the condenser 22 is connected to a diode 21 and a resistor 29. A condenser 25 is arranged nected in the cathode circuit of an amplifier tube directlyfrom condenser 25, so that in case a positive film having black strips between the images is scanned the resulting characteristic curve of amplifiers .31 and 38 is made linear, while it iscurved and changed in its direction when a negative filmis scanned.

. The transparency of the strips between-the images of a negative film is not the same in all films. In order to obtain a control voltage which is independent of the degree of transparency, the value of the control voltage produced at the condenser 25 is limited by an amplitude 29. The anode of this amplifier tube 29 is connected to the positive terminal of a source of potential, while the grid 30 of this tube is connected by lead 3| to a source of negative impulses of the form represented at 32 having substantially rectangular form. The condenser 25 is connected by way of a diode 33 and a source of potential 34 to ground. The condenser 25 is furthermore connected by a lead 40 to the grid 39 of a hexode 31. This hexode is arranged in parallel with a second hexode 38. The output circuit of the image tube is connected by way of a lead 24 and an amplifier 36 to the input circuit of tubes 31 and 38. The output circuit of these two hexodes is'so arranged that one of the tubes has a positive and the other a negative slope, so that one of the tubes produces a phase-correct amplification while the other tube produces a counter-phase amplification. The common output circuit of both tubes includes a resistor 4| connected between ground and the input circuit of an additional amplifier 42.

The operation of this device is as follows: The image signals are amplified in tube l8 and applied by way of condenser 22 to the anode of diode 21. During the image scanning period no current flows through the diode 21 on account of the positive voltage applied to the grid of the tube 29. The diode 21 is only operating during the retrace periods of the field scanning system,

. that is, during the time represented by the negative impulse 32. During this period the strip between successive images is scanned and the,

condenser 25 receives a potential value which depends upon the signal voltage produced by the image tube during this period. The potential of condenser. 25 depends therefore on whether a white or black portion of the film isscanned during this time. As long as diode 21 is passing no current the voltage taken off at tube l8 cannot change the potential of condenser 25. This potential depends therefore only on the character of the portion of the film which scanned during the retract period of the frame scanning system.

The image signals are furthermore applied over lead 24 to the control grids of tubes 31 and 33. The anode of tube 31 and the screen grid of tube 38 situated in front of the distribution grid filter consisting of the diode 33 and the source of potential 34. The voltage of the source 34 is so chosen that the amplitude filter is made to operate if a minimal amount of light passes through the film during the retrace period of the frame deflecting system. The frequency band for the amplifier 18 can be comparatively A further embodiment is represented in Fig.

3 of the drawings. In this embodiment the circuit arrangement up to condenser 25 remains the same as in Fig. 2. Leads 24 and 40, however, are connected to an amplifier of different construction.- Lead 24 is connected by way of an amplifier 35 and a condenser 53 to the grid of an amplifier tube 54. .This amplifier tube has a curved characteristic showing the anode current as a function of grid voltage as represented in Fig. 4. The anode of this tube is connected to an output resistor 52 and at the same time to the contact 48 of a relay 45. The contact 45 of this relay is connected to the output terminal 55 of the amplifier. The cathode of the tube 54 is grounded through a resistor 50 and connected to contacts 49 of the relay 45. Contact 41 of the relay is grounded through a condenser 5|. The winding of the relay 45 is connected in the anode circuit of an amplifier tube 44 the grid of which is connected by lead 48 to the condenser 25 of Fig. 2. If anegative film is scanned the relay 45 is actuated, so that contacts 41 and 49 are closed and contact 48 is connected with the output terminal 55. The amplified impulses are taken off at the anode resistor 52 of, for example, 1,000 ohms, while the cathode resistor 50 is bridged by the condenser 5|. If now a positive film is scanned the relay 45 is de-energized so that the output terminal 55 is connected to the cathode of tube 54 while at the same time the connection to condenser 5| is broken, .so that the signals are derived from resistor 50. In this position of the contacts the tube 54 operates as a cathode amplifier having a linear characteristic curve according to Fig. 5. This arrangement has therefore the effect that not only the phase is changed by but also the characteristic curve or the amplifier is changed.

This circuit can be used in arrangements containing more than one amplifying tube so that the characteristic curve of a number of tubes can be combined to produce the desired eflect.

The invention is not limited to the transmission of negative and positive films, but it can be employed in all cases in which a transmission channel shall have alternatively a curved characteristic and a straight characteristic.

Instead of producing the control voltage from a part of the scanning currents, it may be preferable to arrange a separate photoelectric cell in such a manner behind the film that the light produced by a suitable source of light must pass through a portion of the film before reaching the photocell. The light may pass through an edge portion or through the strip between successive images in case the film is moved intermittently. The output voltage of the photocell is used as the control voltage after suitable amplification.

What I claim is:

1. The method oi controlling the transmission of images of positive and negative character comprising the steps of scanning said images, deriving image signals, deriving control voltages from strips between said images, said strips and said control voltages being indicative oi-- the positive or negative character of said images,

and controlling the phase of the image signals in accordance with said control voltage.

2. The method of controlling the transmission of images of positive and negative character comprising the steps of scanning said images, deriving image signals, deriving control voltages from strips between said images, said strips and said control voltages being indicative of the positive or negative character of said images and controlling thephase and gradation of the signal currents produced by scanning in accordance with said control voltage.

. 3. The method of controlling the transmission of images of positive and negative character comprising the steps of scanning said images to produce picture signals, deriving a control voltage from a portion of said picture signals, said control voltage being indicative of said character of said images, applying said control voltage to a control member adapted to select one of two amplification channels, and amplitying the picture signals derived from positive images in one of said channels and the picture signals derived from negative images in the other of said channels.

4. The method of controlling the transmission of fllmsof positive and negative character comprising the steps of scanning said film images to produce picture signals, deriving a control voltage from the strip of the film between said images, said control voltage being indicative of said character of said images, amplifying said picture image signals, and controlling the phaseand gradation of said picture signals under the influence of said control voltage.

5. In a television system means for scanning images of positive and. negative character to produce image signals, means for deriving a control signal from a strip between each of said images, said portions being representative ofthe positive or negative character of said images, means for amplifying said image signals and means responsive to said control signals for controlling the phase and the linearity of amplification of said image signals.

6. In a television transmission system, means for scanning film images of positive and negativecharacter to produce picture signals and for scanning the strip between adjacent film images, means for deriving a control potential from the scanning of said strip, said control potential being indicative of the character'of said images and an amplifier comprising a, control grid connected to the source of said control potential for changing the phase of said picture signals in accordance with the character of said control potential.

7. In a television transmission system, means for scanning alternatively film images of positive and negative character to produce picture signals, means for scanning the strip between adja-' cent film images, means for deriving a control potential from the scanning of said strip, said control potential being indicative of said character of said images, an amplifier arrangement for amplifying said picture signals including two amplifier tubes connected in parallel, one of said tubes having a negative and the other a positive slope of the characteristic curve, and a grid in one of said tubes connected to the source of control potential.

8. In a television transmission system, means for scanning alternatively film images of positive and negative character to produce picture signals, means for scanning the strip between adjacent film images, means for deriving a control potential. from the scanning of said-strip, an amplifier for ampli ying said picture signals,

a relay adapted to be actuated by said control potential, a plurality of contacts actuated by said relay for connecting the output terminal of said picture signal amplifier alternatively to the anode circuit and the cathode circuit of said picture-signal amplifier in accordance with said control potential.

9. In a television transmission system, means for scanning alternatively film images of positive and negative character to produce picturesignals, means for scanning the strip between adjacent film images, means for deriving a control potential from the scanning of said strip, an amplifier for amplifying said picture signals, a relay adapted to be actuated by said control potential, a plurality of contacts actuated by said relay for connecting the output terminal of said picture signal amplifier alternatively to the anode circuit and the cathode circuit of said picture-signal amplifier in accordance with said control potential, and means for bridging the cathode resistance by a condenser when said output terminal is connected to the anode circult of said picture-signal amplifier.

-WOLFGANG DILLENBURGER. 

